文章标题

1. Comparator 和 Comparable 相同的地方

他们都是java的一个接口, 并且是用来对自定义的class比较大小的,

什么是自定义class: 如 public class Person{ String name; int age }.

当我们有这么一个personList,里面包含了person1, person2, persion3….., 我们用Collections.sort( personList ),
是得不到预期的结果的. 这时肯定有人要问, 那为什么可以排序一个字符串list呢:

如 StringList{“hello1” , “hello3” , “hello2”}, Collections.sort( stringList ) 能够得到正确的排序, 那是因为
String 这个对象已经帮我们实现了 Comparable接口 , 所以我们的 Person 如果想排序, 也要实现一个比较器。

2.Comparator 和 Comparable 的区别

Comparable

Comparable 定义在 Person类的内部:

public class Persion implements Comparable {..比较Person的大小..},

因为已经实现了比较器,那么我们的Person现在是一个可以比较大小的对象了,它的比较功能和String完全一样,可以随时随地的拿来
比较大小,因为Person现在自身就是有大小之分的。Collections.sort(personList)可以得到正确的结果。

Comparator

Comparator 是定义在Person的外部的, 此时我们的Person类的结构不需要有任何变化,如

public class Person{ String name; int age },

然后我们另外定义一个比较器:

public PersonComparator implements Comparator() {..比较Person的大小..},

在PersonComparator里面实现了怎么比较两个Person的大小. 所以,用这种方法,当我们要对一个 personList进行排序的时候,
我们除了了要传递personList过去, 还需要把PersonComparator传递过去,因为怎么比较Person的大小是在PersonComparator
里面实现的, 如:

Collections.sort( personList , new PersonComparator() ).

public class CompareTest {    public static void main(String[]args){        List<Student>list = new ArrayList<Student>(10);        list.add(new Student(1,"jj"));        list.add(new Student(0,"kj"));        list.add(new Student(0,"kk"));        list.add(new Student(0,"kw"));        list.add(new Student(2,"ll"));        System.out.println(list);        Collections.sort(list);        System.out.println(list);        List<Teacher>t = new ArrayList<Teacher>(10);        t.add(new Teacher(1,12));        t.add(new Teacher(0,13));        t.add(new Teacher(0,14));        t.add(new Teacher(2,15));        t.add(new Teacher(2,16));        System.out.println(t);        Collections.sort(t,new TeacherComparator());        System.out.println(t);    }}class Student implements Comparable{    int num;    String name;    public Student(int num,String name){        this.num = num;        this.name = name;    }    @Override    public String toString() {        return "Student{" +                "num=" + num +                ", name='" + name + '\'' +                '}';    }    @Override    public int compareTo(Object o) {        Student stu = (Student)o;        int result = stu.num>num?1:(stu.num==num?0:-1);        if (result==0){           // result = stu.name.indexOf(0)>name.indexOf(0)?1:-1;            result = stu.name.compareTo(name);        }        return result;    }}class Teacher{    int num;    double salary;    public Teacher(int num,double salary){        this.num = num;        this.salary = salary;    }    @Override    public String toString() {        return "Teacher{" +                "num=" + num +                ", salary=" + salary +                '}';    }}class TeacherComparator implements Comparator{    @Override    public int compare(Object o1, Object o2) {        Teacher t1 = (Teacher)o1;        Teacher t2 = (Teacher)o2;        int result = t1.num<t2.num?1:(t1.num==t2.num?0:-1);        return result=result==0?(t1.salary<t2.salary?1:-1):result;    }}

输出：

[Student{num=1, name='jj'}, Student{num=0, name='kj'}, Student{num=0, name='kk'}, Student{num=0, name='kw'}, Student{num=2, name='ll'}]---------------[Student{num=2, name='ll'}, Student{num=1, name='jj'}, Student{num=0, name='kw'}, Student{num=0, name='kk'}, Student{num=0, name='kj'}]---------------

*****************[Teacher{num=1, salary=12.0}, Teacher{num=0, salary=13.0}, Teacher{num=0, salary=14.0}, Teacher{num=2, salary=15.0}, Teacher{num=2, salary=16.0}][Teacher{num=2, salary=16.0}, Teacher{num=2, salary=15.0}, Teacher{num=1, salary=12.0}, Teacher{num=0, salary=14.0}, Teacher{num=0, salary=13.0}]*****************